High pressure pump

ABSTRACT

A piston ( 6 ) of a piston pump unit ( 2 ), which can be displaced in a translatory manner, is guided in a cylinder bore ( 7 ). The piston ( 6 ) is driven by a crank drive ( 13 ) comprising an eccentric element ( 15 ) which is arranged on a drive shaft ( 14 ). A stroke ring ( 12 ) is rotationally mounted on the eccentric element ( 15 ) but does not rotate therewith. A sliding surface ( 10 ) of the piston ( 6 ) is arranged on a sliding bearing surface ( 11 ) on the stroke ring ( 12 ). A discharge chamber ( 22 ) is embodied inside the piston ( 6 ) on an end opposite the stroke ring ( 12 ). Said discharge chamber is open towards the sliding bearing surface ( 11 ). The discharge chamber ( 22 ) is connected in a pressure-wise manner to a working chamber ( 8 ) by means of a passage ( 23 ) in the piston ( 6 ). A displaceable control piston ( 25 ) is guided in a longitudinal bore ( 24 ) pertaining to said passage ( 23 ). Said control piston ( 25 ) is impinged upon on one side by a medium in the working chamber ( 8 ) and on the other front side by a pressure medium in the discharge chamber ( 22 ). The control piston ( 25 ) separates the medium which is to be transported from the pressure medium in the discharge chamber ( 22 ) and ensures that the pressure in the discharge chamber ( 22 ) increases if the pressure increases in the working chamber ( 8 ). This results in decompression of the sliding bearing between the piston ( 6 ) and the stroke ring ( 12 ).

The invention relates to a high pressure pump according to the preambleof claim 1, which is suitable in particular for use in a fuel injectionsystem for internal combustion engines.

In DE-A-197 05 205 and the corresponding U.S. Pat. No. 6,077,056, ageneric high pressure pump for a fuel injection device for internalcombustion engines is described in which the piston of a piston pumpunit is driven harmonically by an eccentric drive. At its end facingaway from the working chamber of the piston pump unit, the piston bearsa sliding shoe which rests with a sliding surface against a slidingbearing surface of a stroke ring. The stroke ring is rotatably mountedon an eccentric journal of a drive shaft and is driven rotatably butdoes not rotate. The drive shaft, the eccentric journal, the stroke ringand the sliding shoe are all accommodated in a low pressure chamber,which is used as a feed chamber for the medium to be delivered, that isto say fuel. Formed in the sliding shoe is a relief chamber, which isopen toward the sliding bearing surface and has a direct hydraulicconnection to the working chamber via a passage which extends in thelongitudinal direction of the pump piston. The relief chamber isaccordingly filled with the fuel to be delivered.

During the delivery stroke of the piston pump unit, the piston and thesliding shoe fixed to the latter are pressed against the stroke ring bythe pressure acting in the working chamber. At the same time, there isalso an increase in the pressure in the relief chamber connected to theworking chamber, as a result of which the force acting on the slidingshoe and directed away from the stroke ring is increased. Relief of theload on the sliding bearing between the sliding shoe and the stroke ringis therefore achieved. This hydrostatic relief of the load on thesliding bearing leads to a reduction in the friction between the slidingsurface on the sliding shoe and the sliding bearing surface on thestroke ring.

The lubrication of the sliding bearing between the sliding shoe and thestroke ring is carried out by the fuel in the relief chamber. Thebearing between the eccentric journal and the stroke ring is lubricatedby the fuel in the low pressure chamber. However, as is known, fuel haspoor lubricating properties and is therefore able to develop only arestricted lubricating action.

The present invention is, then, based on the object of providing a highpressure pump of the type mentioned at the beginning for very highdelivery pressures and large delivery quantities, whose production costsare as low as possible and which is able to satisfy high requirements onthe operational reliability and on the lifetime.

This object is achieved by a high pressure pump having the features ofclaim 1.

The relief chamber is divided off from the working chamber by thepressure transmission element arranged in the passage in the piston.Therefore, the medium to be delivered, which is fuel, for example, isalso separated from the medium in the relief chamber. There is thus nolonger any restriction to using the medium to be delivered for thepressure relief and the lubrication of the sliding bearing between thestroke ring and the piston. Instead, a medium which is much moresuitable for these tasks can be chosen, which means one with excellentlubricating properties, for example lubrication oil. With theconsiderably improved lubrication of the sliding bearing and also thebearing between the stroke ring and the crank drive, the risk of thesebearings seizing, even under high loading, is reduced sharply, which inturn contributes to increased operational reliability and a longlifetime.

Since the pressure transmission element is pressurized on one side bythe medium to be delivered and can be displaced in the direction of theapplication of pressure, the pressure in the working chamber istransmitted to the medium in the relief chamber, that is to say, whenthe pressure in the working chamber rises, the pressure in the reliefchamber also rises. Therefore, relief of the load on the sliding bearingbetween stroke ring and piston is achieved which becomes greater as thedelivery pressure becomes greater, as is known from the aforementionedprior art. This relief of the load on the sliding bearing not onlypermits higher delivery pressures but also allows an enlargement of thepiston area and therefore an increase in the delivery rate without thenumber of piston pump units necessarily having to be increased for thispurpose. This has a beneficial effect on the production costs.

Preferred further refinements of the high pressure pump according to theinvention form the subject matter of the dependent claims.

In the following text, by using the drawings, exemplary embodiments ofthe subject matter of the invention will be explained in more detail. Inthe drawings, purely schematically:

FIG. 1 shows a first embodiment of a high pressure pump having twopiston pump units, in a longitudinal section,

FIGS. 2 and 3 show one of the two piston pump units with the pump pistonin various operating positions, in an illustration corresponding to FIG.1 and on an enlarged scale,

FIG. 4 shows a section along the line A-A in FIG. 3, and

FIG. 5 shows a second embodiment of a high pressure pump in anillustration corresponding to FIG. 2.

The high pressure delivery pump 1 shown in FIGS. 1-4, which is intendedfor use in a fuel injection system for internal combustion engines, hastwo mutually diametrically opposite piston pump units 2, 2′ (plungerpump units), which are constructionally identical and operate inantiphase. Each piston pump unit 2, 2′ has a housing block 3, which isfirmly connected to a pump casing 4 and projects into the interior 5 ofthis pump casing 4. Each piston pump unit 2, 2′ has a piston 6(plunger), which is guided such that it can move linearly with a closesliding fit in a cylinder bore 7 in the housing block 3. With one endface 6 a, the piston 6 delimits a working chamber 8 and, at its oppositeend, widens to form a base part 9. This base part 9 has a flat slidingsurface 10, which rests on a sliding bearing surface 11 which isprovided on a stroke ring 12. This stroke ring 12 is common to bothpiston pump units 2, 2′. Provided for the harmonic drive of the pistons6 of the two piston pump units 2, 2′ is a crank drive 13, which has adrive shaft 14, illustrated dashed, and an eccentric element 15 firmlyconnected to the latter. The drive shaft 14 is driven in rotation aboutits axis of rotation 14 a (FIG. 1). The stroke ring 12 is seatedrotatably but not so as to corotate on the eccentric element 15. Theeccentric element 15 is arranged with an eccentricity e (FIG. 1) withrespect to the axis of rotation 14 a of the drive shaft 14. Duringrotation of the drive shaft 14, the stroke ring 12 is moved firstlyparallel to the sliding bearing surfaces 12 and secondly at right anglesto the axis of rotation 14 a of the drive shaft 14, specifically by theamount 2 e in each direction. During operation, the stroke ring 12 isthus displaced to and fro with respect to the base part 9 of the piston6. The pistons 6 of the piston pump units 2, 2 a execute a stroke whichis likewise 2 e, that is to say twice the eccentricity e.

Seated on the base part 9 of the piston 6 is a bearing ring 16, which isused as an abutment for a compression spring 17 which is supported atthe other end on the housing block 3. The compression spring 17 keepsthe associated piston 6 in continuous contact with the stroke ring 12.

Formed in the housing block 3 is an inlet conduit 18, which is connectedto the working chamber 8 via a pressure-controlled inlet valve 19 (FIG.1). The inlet conduit 18 is connected to a feed line, not illustrated,which is connected to a liquid reservoir, that is to say in the presentcase to a fuel tank, for example via a pre-delivery pump. In the housingblock 3 there is also an outlet conduit 20, which is connected to theworking chamber 8 via a pressure-controlled outlet valve 21 (FIG. 1).The outlet conduit 20 is connected to a high pressure chamber, forexample the common rail of a fuel injection system.

Formed in the region of the sliding surface 10 in the base part 9 of thepiston 6 is a relief chamber 22, which is open toward the slidingbearing surface 11. In the longitudinal direction of the piston 6 thereextends a continuous, coaxial passage 23, which on one side is opentoward the working chamber 8 and on the other side is open toward therelief chamber 22 (the passage 23 could also be placed off-axis).Belonging to this passage 23, whose diameter changes, is a longitudinalbore 24, in which a control piston 25, which serves as a pressuretransmission element, is displaceably guided with a close sliding fit.The control piston 25 rests on a compression spring 26, which issupported at the other end on a spring ring 27 (FIG. 2), which isretained in the piston 6.

Formed in the housing block 3 is an annular groove 28, which extendsaround the piston 6 and is open toward the cylinder bore 7. In thepiston 6 there is a transverse bore 29, which passes through the piston6 and which is connected to the annular groove 28 at both ends.Connected to the annular groove 28 is a discharge conduit 30, whichextends in the housing block 3 and which is connected to a return line,not shown, which leads to a collecting reservoir, which can be the fueltank. Seepage, which is fed back via the discharge conduit 30, collectsin the annular groove 28 in a manner still to be described.

The eccentric element 15 is provided with a lubricating groove 31, whichextends along a part of the circumference and is open toward the strokering 12. The lubricating groove 31 is connected via a radial bore 32 inthe eccentric element 15 to a feed duct 33, which extends in thedirection of the axis of rotation 14 a of the drive shaft 14 and whichis connected to a lubricant reservoir via a lubricant pump, not shown.Via this feed duct 33, a lubricant, preferably lubricating oil, issupplied at a pressure of, for example, 2-6 bar. Formed in the strokering 12 are two connecting ducts 34, 35, each of which leads from theinner surface 12 a of the stroke ring 12 to one of the sliding bearingsurfaces 11. The lubricating groove 31, which is permanently connectedto the feed duct 33, is, however, connected to a connecting duct 34, 35only in specific rotational positions of the eccentric element 15, ascan be seen from FIGS. 1-3.

The functioning of the high pressure pump 1 will now be described inmore detail by using FIGS. 1-4.

FIG. 1 shows that rotational position of the eccentric element 15 inwhich the piston 6 of the one piston pump unit 2, the upper one in thefigures, is located in the lower end position, that is to say at the endof the suction stroke. The piston 6 of the other, lower piston pump unit2′ has reached the end of the delivery stroke and therefore its upperend position. The connecting ducts 34, 35 are connected neither to thelubricating groove 31 nor to the associated relief chamber 22.

Starting from this initial position, only the operation of the upperpiston pump unit 2 will be described below. The operation of the other,lower piston pump unit 2′ is equal but opposite.

If the drive shaft 14 rotates in the counterclockwise direction, thenthe delivery stroke begins for the piston 6 of the upper piston pumpunit 2, that is to say the piston 6 will be displaced upward in thedirection of the arrow A (FIG. 2). During this delivery stroke, theinlet valve 19 is closed, which also applies to the outlet valve 21 atthe beginning of the delivery stroke. The pressure in the workingchamber 8 rises, the control piston 25, which is pressurized on its endface facing the working chamber 8 by the pressure of the liquid in theworking chamber 8, is moved downward in the direction of the arrow D inFIG. 2, counter to the action of the compression spring 26. The resultof this is that the pressure of the lubricant which is located in therelief chamber 22 and in the region of the passage 23 underneath thecontrol piston 25 is increased. As a result, a force is exerted on thepiston 6 which is directed away from the stroke ring 12 and whichcounteracts the force exerted on the piston 6 by the liquid in theworking chamber 8. In this way, hydrostatic relief of the load on thesliding bearing formed by the sliding surface 10 on the base part 9 andthe sliding bearing surface 11 on the stroke ring 12 is achieved, asdescribed in DE-A-197 05 205 and U.S. Pat. No. 6,077,056 alreadymentioned. An optimum relief action is achieved when the diameter DA ofthe relief chamber 22 is slightly smaller than the diameter DP of theend face 6 a of the piston 6 which faces the working chamber 8 (see FIG.2).

The situation following a rotation of the drive shaft 14 through 900 isillustrated in FIG. 2. The piston 6 has reached its middle positionduring the delivery stroke. There is no connection between thelubricating groove 31 and the relief chamber 22 of the upper piston pumpunit 2. By contrast, in the lower piston pump unit 2′, not shown, therelief chamber 22 is connected to the lubricating groove 31. After therotation of the drive shaft 14 through 90°, illustrated in FIG. 2, thestroke ring 12 assumes its right-hand end position, which is illustrateddashed in FIG. 4 and is designated 12′.

As soon as the pressure in the working chamber 8 in the course of thedelivery stroke of the piston reaches a value which is greater than theclosing force of the outlet valve 21, the latter is opened and theliquid is expelled from the working chamber 8 into the outlet conduit 20and then into the high pressure chamber.

Following a rotation of the drive shaft 14 through 180° from theposition shown in FIG. 1, the delivery stroke of the piston 6 iscompleted. The piston 6 is then moved downward in the oppositedirection, that is to say in the direction of the arrow B (FIG. 3), forthe suction stroke. During this suction stroke, the outlet valve 21remains closed. During the downward movement of the piston 6 in thedirection of the arrow B, a negative pressure is produced in the workingchamber 8, which results in the inlet valve 19 opening and allowingliquid to flow into the working chamber 8. The pressure prevailing inthe relief chamber 22 and the region of the passage 23 underneath thecontrol piston 28, together with the compression spring 26, effectsupward displacement of the control piston 25 in the direction of thearrow E (FIG. 3). The situation following the rotation of the driveshaft 14 through a total of now 270° is illustrated in FIG. 3. Thepiston 6 has reached its middle position during the suction stroke. Thestroke ring 12 now assumes its left-hand end position, which isillustrated by continuous lines in FIG. 4. This FIG. 4 reveals that thestroke ring 12 executes a total stroke C in the direction of the slidingbearing surface 11 which is equal to 2e, that is to say twice theeccentricity e. In this left-hand end position of the stroke ring 12,shown in FIGS. 3 and 4, the connecting duct 34 in the stroke ring 12 isnow connected to the relief chamber 22 and the lubricating groove 31.This means that pressurized oil can get into the relief chamber 22 viathe feed duct 33, the radial bore 32, the lubricating groove 31 and theconnecting duct 34. In this way, the lubricant which has been lostduring the delivery stroke as a result of leakage along the slidingbearing surface 11 and along the outer surface of the control piston 25is replaced.

Following a rotation of the drive shaft 14 through a total of 360°, thepiston 6 is located at the end of the suction stroke and assumes thelower end position illustrated in FIG. 1 again. The operating cycledescribed starts from the beginning.

Although the piston 6 is guided in the cylinder bore 7 with a closesliding fit, on the one hand liquid, that is to say fuel, can passthrough the gap between the piston 6 and the wall of the cylinder bore 7and, on the other hand, lubricant, that is to say lubricating oil, canpass out of the interior 5 of the pump casing 4. This seepage iscollected in the annular groove 28 as a liquid-lubricant mixture, thatis to say as a fuel-lubricating oil mixture.

In addition, it is possible that liquid (fuel) can pass out of theworking chamber 8 via the upper section of the passage 23 and throughthe very small gap between the control piston 25 and the wall of thelongitudinal bore 24. This seepage likewise passes into the annulargroove 28 via the transverse bore 29 in the piston 6. Furthermore,lubricant (lubricating oil) from the relief chamber 22 can pass throughthe narrow gap between the control piston 25 and the wall of thelongitudinal bore 24. This leakage lubricant likewise passes into theannular groove 28 via the transverse bore 29.

The mixture of liquid (fuel and lubricant (lubricating oil)) in theannular groove 28 is led away via the discharge conduit 30 and, forexample, led back into the liquid reservoir, that is to say the fueltank.

In the following text, a variant of the embodiment shown in FIGS. 1 and2 will be described in which, in the base part 9 of the piston 6, in theregion of the sliding surface 10, an annular groove 36 is additionallyformed, which is arranged coaxially with respect to the relief chamber22 and is open toward the sliding bearing surface 11. This annulargroove 36 is connected to a longitudinal groove 37 which is formed inthe stroke ring 12 and which is open toward the sliding surface 10. Thislongitudinal groove 37 is offset with respect to the section plane ofFIG. 3 (which extends at right angles to the axis of rotation 14 a andin the center of the stroke ring 12) in the direction of the axis ofrotation 14 a of the drive shaft 14 and opens into the interior 5 of thepump casing 4 at both ends (FIG. 4). The seepage (lubricating oil)entering this annular groove 36 is led back into the interior 5 via thelongitudinal groove 37.

As a result of the provision of the annular groove 36, the pressuredistribution on the sliding surface 10 and the sliding bearing 37 in theradial direction toward the outside from the relief chamber 22 ischanged, which has a beneficial influence on the amount of the seepage.

The second embodiment of a high pressure pump 1′, shown in FIG. 5,differs from the first embodiment according to FIGS. 1-4 through adifferent configuration of the pressure transmission element arranged inthe piston 6. In this FIG. 5, which in terms of illustration correspondsto FIG. 2, the same designations as in FIGS. 1-4 are used for partswhich are the same in both embodiments.

In this second embodiment according to FIG. 5, the piston 6 comprises apiston element 38 guided in the cylinder bore 7 and a ring 39, which isfirmly connected to the piston element 38 at the end of the latterfacing away from the working chamber 8, for example by being pressed onor shrunk on. The ring 39 rests with a sliding surface 10 on the slidingbearing surface 11 on the stroke ring 12 and has a flange 40, on whichthe compression spring 17 is supported. As described by using FIGS. 1-3,this compression spring 17 ensures that the ring 39 remains in contactwith the stroke ring 12. The sliding surface 10 is formed on the ring39. The flange 40 could also be formed as a separate part, analogous tothe bearing ring 16 of FIG. 2.

Arranged between the ring 39 and the piston element 38 is a diaphragm 41which can be deflected elastically and is clamped firmly in a sealingmanner along its edge region between the ring 39 and the piston element38. This diaphragm 41, serving as a pressure transmission element, spansthe relief chamber 22 delimited by the inner wall 39 a of the ring anddivides this relief chamber 22 from a chamber 42 formed in the pistonelement 38. Into this chamber 42 there opens a longitudinal bore 43,which extends in the direction of the longitudinal axis of the pistonelement 38 and via which the chamber 42 is connected to the workingchamber 8. The longitudinal bore 43 and the chamber 42 form the passage23. The chamber 42 is filled with the liquid to be delivered, that is tosay with fuel.

The pressure in the chamber 42 changes in the same direction as thepressure in the working chamber 8. With increasing pressure in thechamber 42, the diaphragm 41 is deflected downward in the direction ofthe application of pressure, that is to say toward the sliding bearingsurface 11. This leads to an increasing pressure in the relief chamber22 containing lubricant, and therefore to hydrostatic pressure relief,as has already been described by using FIGS. 1-4. Since the pressures onboth sides of the diaphragm 41 are virtually identical, the stressing ofthe diaphragm 41 is low. The latter can therefore be thin-walled andelastic.

In the variant according to FIG. 5, the annular groove 28 together withdischarge conduit 30 for collecting and leading seepage away, present inthe first exemplary embodiment according to FIGS. 1-3, is not shown butcan likewise be provided if required.

In a further variant, not illustrated, the diaphragm 41 is fitted to theend surface 6 a of the piston 6 facing away from the working chamber 8.The diaphragm 41 could be fixed by welding the same on or, in a manneranalogous to that in FIG. 5, could be fixed with a screwed, pressed orshrunk retaining part. The passage 23 is then located underneath thediaphragm 41, it is filled with the lubricant and communicates directlywith the relief chamber 22.

The action of the embodiment illustrated in FIG. 5 corresponds to themode of operation described by using FIGS. 1-4.

The exemplary embodiments of a high pressure pump 1, 1′ according to theinvention, described in conjunction with FIGS. 1-5, have the advantagethat, as a result of arranging a pressure transmission element, that isto say a control piston 25 or diaphragm 41, in the passage 23 connectingthe working chamber 8 and the relief chamber 22, the media in theworking chamber 8 and in the relief chamber 22 are separated from eachother. This permits the use of a suitable lubricant in the region of thestroke ring 12 and of the crank drive 13, irrespective of the medium(fuel) to be delivered. In addition, without great constructionalexpenditure, the desired pressure relief of the sliding bearing which isformed by the sliding surface 10 of the piston 6 and the sliding bearingsurface 11 on the stroke ring 12 is achieved.

It goes without saying that various variants of the exemplaryembodiments shown are possible. Reference will be made to some of thesevariants below.

In a further embodiment, the piston 6 has no transverse bore 29. Becauseof the close sliding fit and the pressure relationships achievedaccording to the invention on both sides of the control piston 25, theleakage from the side facing the working chamber 8 into the reliefchamber 22 can be kept very low.

Under certain circumstances, it is also possible to dispense withmeasures for collecting and discharging seepage along the outside of thepiston 6, that is to say to dispense with the annular groove 28 and thedischarge conduit 30 in the housing block 3, if no noticeable leakageoccurs as a result of the prevailing pressure conditions.

In a further variant, not illustrated, the control piston 25 has alarger diameter than illustrated in FIGS. 1-3. The longitudinal bore 24for guiding the control piston 25 with a close sliding fit can be openat the top in the direction of the working chamber 8. In this case, thepart of the passage 23 which has a narrower cross section is againlocated under the control piston 25 and communicates directly with therelief chamber 22. The control piston 25 is installed in the piston 6from above. A spring ring, analogous to the spring ring 27 according toFIG. 2, then prevents the control piston emerging above the end surface6 a. The longitudinal bore 24 can also be continuous in the piston 6. Inthis case, the remaining part of the passage 23 has the same diameter asthe longitudinal bore 24. It is also conceivable to form the remainingsection of the passage 23 slightly larger than the diameter of thelongitudinal bore 24.

Furthermore, there is also a need to keep the lubrication losses fromthe relief chamber 22 into the interior 5 of the housing low. One meansfor this purpose is illustrated in the embodiment of FIGS. 3 and 4(annular groove 36 and longitudinal groove 37). If the flat slidingsurface 10 of the base part 9 and the sliding surface 11 of the strokering 12 do not rest exactly on each other, for example because of aforced skewed position of the two sliding surfaces 10 and 11, thelubrication losses are detrimentally affected. Constructional measuresfor preventing such a state can be: forming the base part 9 with acertain elasticity, such that the sliding surface 10 can adapt to thesliding surface 11 by means of slight elastic deformation of the basepart 9. Division of base part 9 and piston 6 into two parts, in a manneranalogous to that in DE-A-197 05 205 and the corresponding U.S. Pat. No.6,077,056 in FIG. 4, can also be applied. In addition, the inner surface12 a of the stroke ring 12, together with the associated surface of theeccentric element 15, could be slightly convex in the direction of theaxis of rotation 14 a or even slightly spherical in the longitudinal andtransverse direction. In this case, it is recommended to configure thestroke ring 12 in two parts for installation reasons.

Instead of two piston pump units 2, 2′, as shown in FIG. 1, only onepiston pump unit 2 can also be provided. Conversely, more than twopiston pump units with corresponding sliding surfaces 11 of the strokering 12 can also be fitted radially, for example 3 piston pump unitsoffset by 120°, or 4 offset by 90°, or 6 offset by 60°, with a commonstroke ring 12.

In addition, it is also possible to arrange two or more individualpiston pump units or two or more pairs of mutually opposite piston pumpunits 2, 2′ operating in antiphase one after another in the direction ofthe axis of rotation 14 a of the drive shaft 14.

Although the high-pressure pumps 1, 1′ described are provided for use infuel injection systems of internal combustion engines, in particular ofdiesel engines, these pumps can also find applications in other fields.

It is also possible to dispense with the compression spring 26 and thespring ring 27 supporting the latter. In this case, the control piston25 is moved solely by the compressive forces acting on the two ends.

Finally, it is also possible to form the control piston 25 with twodifferent diameters. Then, if the end face facing the working chamber 8is larger than that facing the relief chamber, a step up in pressuretakes place; in the opposite case a step down in pressure. In the caseof these refinements, it may be advantageous to form the control piston25 from two separate parts each having the appropriate diameter. If thebore having the correspondingly larger diameter and that having thecorrespondingly smaller diameter are not aligned exactly, tolerance andfriction problems can be prevented in this way.

1-16. (canceled)
 17. A high pressure pump, in particular for a fuelinjection system for internal combustion engines, having at least onepiston pump unit (2, 2′) which has a piston (6) guided in a cylinderbore (7) and delimiting a working chamber (8), having a crank drive (13)for driving the piston (6), having a stroke ring (12) which is arrangedbetween the crank drive (13) and the piston (6) and which is mountedsuch that it is driven rotatably with respect to the crank drive (13)but does not rotate and which has a flat sliding bearing surface (11),on which the piston (6) is supported with a sliding surface (10), andhaving a relief chamber (22) which is arranged in the region of thesliding surface (10), is open toward the sliding bearing surface (11)and which has a pressure connection to the working chamber (8) via apassage (23) formed in the piston (6), characterized in that in thepassage (23) in the piston (6) there is arranged a pressure transmissionelement (25, 41), which can be pressurized on one side by the medium tobe delivered and on the opposite side by a pressure medium in the reliefchamber (22), can be displaced in the direction of the application ofpressure under the action of pressure and separates the relief chamber(22) fluidically from the working chamber (8).
 18. The high pressurepump as claimed in claim 17, wherein the crank drive (13) has aneccentric element (15) which is arranged on a rotatably driven driveshaft (14) with an eccentricity (e) and on which the stroke ring (12) ismounted such that it does not corotate.
 19. The high pressure pump asclaimed in claim 17, wherein the pressure transmission element is acontrol piston (25), which can be displaced in a longitudinal bore (24)belonging to the passage (23) and is guided closely in a sliding manner.20. The high pressure pump as claimed in claim 19, wherein, on its endfacing the relief chamber (22), the control piston (6) is supported on acompression spring (26) which rests on an abutment at the other end. 21.The high pressure pump as claimed in claim 20, wherein the abutment isformed by a supporting element retained in the control piston (25), inparticular a spring ring (27).
 22. The high pressure pump as claimed inclaim 17, wherein the pressure transmission element is a diaphragm (41)which can be deflected elastically, which covers the passage (23) and isfixed in a sealing manner in its edge region.
 23. The high pressure pumpas claimed in claim 22, wherein the piston (6) has a piston element (38)guided in the longitudinal bore (7) and a ring (39) which is connectedto the piston element (38) at the end of the latter facing away from theworking chamber (8).
 24. The high pressure pump as claimed in claim 23,wherein the diaphragm (41) is held firmly in its edge region between thepiston element (38) and the ring (39).
 25. The high pressure pump asclaimed in claim 19, wherein in the piston (6) there is formed anannular groove (36) which surrounds the relief chamber (22) and iscoaxial with the latter, which is open toward the sliding bearingsurface (11) and which is connected to a chamber (5) in which the crankdrive (13) and the stroke ring (12) are accommodated.
 26. The highpressure pump as claimed in claim 25, wherein in the stroke ring (12),in the region of the sliding bearing surface (11), there is formed alongitudinal groove (37) which is open toward the sliding surface (10)and opens into the chamber (5), is offset with respect to the reliefchamber (22) in the direction of the axis of rotation (14 a) of thedrive shaft (14) and communicates with the annular groove (36).
 27. Thehigh pressure pump as claimed in claim 17, wherein the pressure mediumin the relief chamber (22) is a lubricant, preferably lubricating oil.28. The high pressure pump as claimed in claim 27, wherein in the strokering (12) there is formed a connecting duct (34, 35), which opens intothe sliding bearing surface (11) at a point such that it is connected tothe relief chamber (22) only in specific positions of the stroke ring(12) with respect to the piston (6) and which can be connectedperiodically to a lubricant feed conduit (31, 32, 33).
 29. The highpressure pump as claimed in claim 28, wherein, at the other end, theconnecting duct (34, 35) opens into the inner surface (12 a) of thestroke ring (12) which is in contact with the eccentric (15) of thecrank drive (13), and in that on the circumference of the eccentric (15)there is provided a lubricating groove (31) which extends over part ofits circumference and is open toward the outside and is connected to alubricant source via a connecting line (32, 33) running in the eccentric(15) and in the drive shaft (14), the lubricating groove 31 beingarranged such that it is connected to the connecting duct (34, 35) inthe stroke ring (12) when this connecting duct (34, 35) is connected tothe relief chamber (22).
 30. The high pressure pump as claimed in claim17, wherein in the wall of the cylinder bore (7) there is formed anannular collecting groove (28) which is open toward the piston (6), isused to collect seepage which passes through the gap between the wall ofthe cylinder bore (7) and the piston (6) and to which a dischargeconduit (30) is connected.
 31. The high pressure pump as claimed inclaim 30, wherein in the piston (6) there is a transverse bore (29)which leads from the longitudinal bore (24) in the piston (6) to theouter wall of the latter, opens into the annular collecting groove (28)and is used to carry away seepage which passes through the gap betweenthe wall of the longitudinal bore (24) and the control piston (25). 32.The high pressure pump as claimed in claim 17, wherein the high pressurepump (1, 1′) is designed to deliver fuel, in particular diesel fuel. 33.The high pressure pump as claimed in claim 17, wherein the piston (6) isprovided at its end opposite the working chamber (8) with a base part(9) in which the relief chamber (22) is formed.
 34. The high pressurepump as claimed in claim 33, wherein the diameter of the relief chamber(22) is bigger than the diameter of the passage (23) in the piston (6).35. The high pressure pump as claimed in claim 34, wherein the diameterof the relief chamber (22) is bigger than the diameter of a longitudinalbore (24) which is part of the passage (23).
 36. The high pressure pumpas claimed in claim 17, wherein the diameter of the passage (23) in thepiston (6) is the same throughout the entire length of the passage (23).